Skin or hair wash compositions are generally made mainly of an anionic surfactant such as an alkyl sulfate or an alkyl sulfonate. These have been excellent in washing power, but problematic in irritation.
Meanwhile, an N-long-chain-acyl amino acid and/or its salt has been known to be useful as a less irritant material. However, this material has not been unsatisfactory at a practical level in some types of amino acids, especially in neutral amino acids in the aspect of foaming or washing power.
In order to improve the foam properties of N-long-chain-acyl neutral amino acid salts for solving this problem, there are an example of mixing an N-long-chain-acyl neutral amino acid salt with a cationic polymer (Patent Document 1: gazette of JP-A-5-156299) and an example of mixing an acyl glycine salt with a chelating agent and a water-soluble high-molecular compound (Patent Document 2: gazette of JP-A-7-331282). These examples have been improved in foam properties of an N-long-chain-acyl neutral amino acid salt, but poor in washing power. Further, there is an example of mixing an N-long-chain-acyl neutral amino acid salt with a nonionic surfactant having a specific structure of HLB of at least 3 but less than 8 for improving washing property of an N-long-chain-acyl neutral amino acid-containing wash (Patent Document 3: gazette of JP-A-5-156288). Although the incorporation of the nonionic surfactant improved the washing function, satisfactory foam properties were not necessarily obtained.
Accordingly, a wash composition using an N-long-chain-acyl amino acid and/or its salt, especially an N-long-chain-acyl neutral amino acid and/or its salt which less irritate(s) the skin or the hair, satisfying both of the high foam properties and the high washing power and having the excellent feeling upon use has been in high demand.
[Patent Document 1] gazette of JP-A-5-156299
[Patent Document 2] gazette of JP-A-7-331282
[Patent Document 3] gazette of JP-A-5-156283